A Light-Emitting Diode (LED), as used herein, is a semiconductor light source for generating a light at a specified wavelength or a range of wavelengths. LEDs are traditionally used for indicator lamps, and are increasingly used for displays. An LED emits light when a voltage is applied across a p-n junction formed by oppositely doped semiconductor compound layers. Different wavelengths of light can be generated using different materials by varying the bandgaps of the semiconductor layers and by fabricating an active layer within the p-n junction.
A phosphor material is usually added to change the properties of light generated by the LED. For example, the monochromatic light provided by an LED can be converted to a polychromatic light through the application of several phosphors, either in a mixture or several phosphor layers. The phosphors Stokes shift blue light or other shorter wavelength light to a longer wavelength. The perception of white may be evoked by generating mixtures of wavelengths that stimulate all three types of color sensitive cone cells (red, green, and blue) in the human eye in nearly equal amounts and with high brightness compared to the surroundings in a process called additive mixing. The white light LED may be used as lighting, such as back lighting for various display devices, commonly in conjunction with a liquid crystal display (LCD).
Traditionally, LEDs are made by growing a plurality of light-emitting structures on a growth substrate. The light-emitting structures along with the underlying growth substrate are separated into individual LED dies. At some point before or after the separation, electrodes or conductive pads are added to each of the LED dies to allow the conduction of electricity through the structure.
Depending on the application in which the light is used, a viewing angle may be specified from which a majority of emitted light must be directed. A generic horizontal LED die emits about half of its light from the top and about half from the sides. LED packaging involves combining the LED die with a reflector structure on a package substrate and forming electrical connections to power and control the final product, which is the optical emitter. A reflector is usually packaged with the LED die to redirect the side emissions and improve total light extraction in a direction away from the package substrate.
While existing methods of packaging an LED have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect. More efficient methods and designs that recycle more of the side emissions and improve control of the resulting light generated at all angles continue to be sought.